Lisp-style C++ template meta programming

That could be pretty cool, I wonder what it does for compile time though.

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I imagine because some of the cool constexpr improvements are only available in C++20 and C++23.

Template metaprogramming isn't really suited for this task, the prime sieve here serves only as a proof of concept, meant to show the capabilities of this style. But there are cases where `constexpr` is not applicable, especially when involving type manipulations.

On the other hand, C++ template metaprogramming, as an esolang, is fun to tame and experiment with.

In my grad school days, a couple of decades ago, I had written a library for my own use to facilitate chaining of different kinds of numeric operations on data vectors and sequences. Essentially, for a very simple form of deforestation [0,1], equipped with intermediate buffers to facilitate SIMD.

GCC, surprisingly, was quite good at generating SIMD code from it and eliminating temporary data vectors. GCC was even quite good at explaining why it didn't emit SIMD that I wanted it to emit. Much to my surprise GCC was better in this regard than Clang. From what I had read about Clang at that time, it should have been the otherway round. The error messages were better too (wonders of competition).

I quite liked it. It was a loads of fun. I would however be wary of using it in anger.

The problem is, this sublanguage feels more like a dynamically typed language where errors would be thrown deep in the instantiation chain when it ultimately failed to instantiate.

There was no type-system to guide you ahead-of-time that what you are trying to do would eventually fail to instantiate.

The code got lost when Bitbucket stopped it's support for Mercurial. I still likely have it somewhere in my old files.

Later I wanted to rewrite this in D but never started (thrown out of my university because I graduated).

[0] https://en.wikipedia.org/wiki/Deforestation_(computer_scienc...

[1] https://en.wikipedia.org/wiki/Expression_templates